Marc-André Brideau

Impacts of the 2007 Landslide-Generated Tsunami in Chehalis Lake, Canada

On 4 December 2007, a 3 Mm3 debris avalanche entered Chehalis Lake, British Columbia, Canada. The resulting tsunami caused extensive shoreline damage as far away as the outlet (7.5 km) and far down lower Chehalis River (>15 km). We documented impacts of the tsunami through a multifaceted investigation that included field surveys and collection and analysis of SONAR data, LiDAR data and high-resolution orthophotographs. Geomorphic impacts included a wide range of erosional and depositional features, many of which provide information on wave energy, direction, run-up and inundation along much of the lakeshore. Our characterization of the geomorphic impacts of the Chehalis Lake event advances understanding of landslide-generated tsunami in several ways: it aids identification of events elsewhere by providing insight into their geomorphic signature; it provides an opportunity to verify hydrodynamic numerical models; and it improves regional understanding of hazard and risk.

Evaluating Kinematic Controls on Planar Translational Slope Failure Mechanisms Using Three-Dimensional Distinct Element Modelling

This paper investigates the importance of kinematic release mechanisms on planar translational slope failure using three-dimensional distinct element codes. The importance of the dip and dip direction of the rear, basal and lateral release surfaces and their influence on failure mechanism, dilation, and the development of step-path failures is illustrated. The three-dimensional block shape and volume of the unstable rock masses simulated with the different discontinuity set geometries are characterized. Two assumed three-dimensional slope models are investigated in order to assess the importance of varying kinematic confinement/release mechanisms. These two assumed boundary conditions are shown to be critical in the development of asymmetrical rock mass deformation patterns. Scale effects due to the block size and discontinuity persistence are shown to control the calculated displacement and failure mechanisms. The numerical modelling results are also demonstrated to be sensitive to the assumed normal and shear stiffness of the discontinuities. The influence of the factors investigated on the failure of a single rock block versus a rock mass are compared and discussed.

Mass Movement in Bedrock

Abstract Bedrock mass movements include some of the most common (rockfalls) and most destructive (rock avalanches) slope processes. The characteristic volumes, velocities, runout distances, and frequencies of bedrock mass movement types can vary over many orders of magnitude. An understanding of the multiple attributes, contributing factors, and processes is required to conduct a comprehensive characterization of the hazards associated with bedrock mass movements. The characterization includes the mechanical properties of intact rock, orientation and surface characteristics of discontinuities, geological history of the rock mass, and topography of the slope, including past and currently active tectonic and geomorphic processes. Conditions of rock–slope stability can be classified into three broad categories based on the factor controlling them: rock structures, intact rock strength, and rock mass strength. Applications of the progressive failure concept are presented to explain the behavior of rock masses leading to a slope failure. The range bedrock mass movement types within Varnes-based landslide classification scheme are also reviewed. Three case studies, Seymareh (Iran), La Clapiere (France), and Threatening Rock (United States), are presented in detail to illustrate the range of bedrock mass movement types and characteristics presented in this chapter. As with mass movements in other material types (snow, ice, soil, and debris), inventory mapping, monitoring, and modeling (numerical and physical) form the basis of bedrock mass movement recognition and anticipation. Avoidance is the simplest and most effective response to rock–slope instabilities as active mitigation is only effective for small volume rockfalls or is only possible at significant economic cost for large slow-moving features. The chapter closes with a review of risk management strategies as applied to bedrock mass movements. The individual components of the risk equation are presented along with examples of responses that could help reduce the calculated risk value.

Introduction: Application of Numerical Modelling Techniques to Landslides

Numerical modelling techniques can be used in conjunction with detailed site investigation and slope monitoring to gain a better understanding of the factors controlling the deformation or failure mechanism of a particular slope. A wide range of numerical modelling techniques are also available to assess the post-failure behaviour of mass movements. The numerical modelling techniques for the pre- or post-failure behaviour of a landslide can be based on empirical relationships, continuum mechanics, or discontinuum mechanics. These techniques have been calibrated based on numerous back-analysis of various mass movement types and can now be used as a numerical laboratory to evaluate the mechanical behaviour of landslide for a variety of scenarios.